1. Field of Invention
The present invention generally relates to a polarization beam combiner, suitable for high-density wavelength multi-functional fiber optic systems. More particularly, the invention relates to the field of optical polarization beam combiners that associate birefringent crystals and wedged crystals.
2. Related Art
As the information technology rapidly progresses, higher performance of optical communication systems is required. For optical communication within short distances, laser techniques may be implemented with satisfactory results. However, the laser techniques do not provide sufficient power for optical communication performed at distances up to 40 kilometers. In this case, the communication system usually must be equipped with erbium-doped fiber amplifiers (EDFA) and Raman amplifiers, which increases the equipment and maintenance costs.
To overcome these problems, an economical solution known in the art combines the light powers of three-ports passive elements that are associated with a laser source to form a high laser-power device capable of providing relatively higher power, similar to the role of EDFA and Raman amplifiers. This equipment further can include the assembly of light-isolating devices to prevent reverse optical noises in the fiber optical communication system, thereby improving the system quality.
U.S. Pat. No. 6,331,913 describes such a system provided with the functions of polarization beam combiner and splitter. However, the disclosed structure has a complex and bulky structure that requires a high manufacturing cost. Moreover, the system disclosed in the U.S. patent does not include reverse isolating characteristics and light isolating devices have to be additionally mounted.
As shown in FIG. 12A–12B, the present application have proposed a technical solution in the U.S. Patent Publication No. 2004/0080827. However, a disadvantage of the assembly disclosed in the U.S. Patent Publication is that the base of the wedged crystal 9 has to be mounted to the birefringent crystal to couple the emerging light beam to a same optical fiber, which increases the manufacture cost. As illustrated in FIG. 12C–12D, the implementation disclosed in U.S. Patent No. 6,643,064 for alternately dividing an optical wavelength encounters the same problems as illustrated in FIG. 12A–12B.